After non-transmural myocardial infarction, the coronary collateral blood flow to non-infarcted subepicardial tissue returns towards normal in the resting state. We studied dogs 3-4 days after non-transmural MI and found that the collateral flow to surviving subepicardium was 56 percent of normal zone subepicardium at rest, but only 35 percent of normal zone during stress induced by pacing tachycardia. These data suggest the potential for stress to induce angina or other ischemic complications in surviving myocardium within the region of supply of an occluded coronary artery.